Jean Dickey of NASA's Jet Propulsion Laboratory, Pasadena:
One possibility is the movements of Earth's core (where Earth's
magnetic field originates) might disturb Earth's magnetic shielding of
charged-particle (i.e., cosmic ray) fluxes that have been hypothesized
to affect the formation of clouds. This could affect how much of the
sun's energy is reflected back to space and how much is absorbed by our
planet. Other possibilities are that some other core process could be
having a more indirect effect on climate, or that an external (e.g.
solar) process affects the core and climate simultaneously.